The ability to redirect cellular processes from proliferation to terminal differentiation offers a promising approach toward preventing cancer progression, and understanding the molecular mechanisms involved in this switch can potentially uncover important targets for early detection of cancer. We have been studying differentiation in non-small cell lung cancer cell lines by three different approaches: 1) Develop model systems of differentiation to enable the study of molecular mechanisms of differentiation control in lung carcinogenesis. We have identified two potential new model systems of epithelial differentiation. Treatment of the NSCLC cell lines H358 and A549 with the tumor promoter mezerein and the tyrosine kinase inhibitor genestein, respectively, results in striking morphologic changes, cell cycle arrest, and growth inhibition suggestive of differentiation. Current studies are examining the relationship between cell cycle control and differentiation. 2) Study differentiation markers and genes controlling differentiation and proliferation in primary lung tumors, premalignant lesions, and cell lines to identify targets for early detection screening. Our initial studies of cJun, a known mediator of tumor promotion, have revealed that whereas normal pulmonary epithelium rarely expresses cJun, 50-90% of atypical/premalignant lesions express cJun. Expression is lower in primary tumors, but cell line analysis reveals that cJun is functional and capable of mediating growth factor signals even under in vitro conditions. These results suggest a role for cJun in early carcinogenesis and a potential role as a target for early detection of lung cancer. 3) Evaluate the function and regulation of the Clara cell protein CC10. Transgenic mouse model systems suggest that CC10 expression is lost early during lung carcinogenesis. Analysis of CC10 mRNA expression (by Northern blot) reveals absent mRNA in 9/10 NSCLC cell lines, although the tumor promoter TPA and serum stimulation induce expression of CC10 in one additional cell line. Studies are underway to determine the mechanisms responsible for suppression of CC10 activity and to understand the biologic relevance of the protein. These studies will shed light on the biology of lung cancer and enable us to identify targets for early detection and intervention as well as potentially develop strategies for enforcing terminal differentiation as a therapeutic goal during lung carcinogenesis.